# coding: utf-8
# 63
import math

a,b,c,d= map(float,input().split())
A = (a-c)**2+(b-d)**2
if A<0:
    A = math.fabs(A)
print(math.sqrt(A))
 import math math a,b,c,d= map(float,input().split()) a map(float,input().split()) map float input().split() ().split () input split b c d A = (a-c)**2+(b-d)**2 A (a-c)**2+(b-d)**2 (a-c)**2 a-c a c 2 (b-d)**2 b-d b d 2 if A<0:
    A = math.fabs(A) A<0 A 0 A = math.fabs(A) A math.fabs(A) math.fabs math fabs A print(math.sqrt(A)) print math.sqrt(A) math.sqrt math sqrt A A = math.fabs(A) math.fabs(A) A b,c,d= map(float,input().split()) map(float,input().split()) b c,d= map(float,input().split()) map(float,input().split()) c d= map(float,input().split()) map(float,input().split()) d a,b,c,d= map(float,input().split()) map(float,input().split()) a A = (a-c)**2+(b-d)**2 (a-c)**2+(b-d)**2 A
# coding: utf-8
# 63
import math

a,b,c,d= map(float,input().split())
A = (a-c)**2+(b-d)**2
if A<0:
    A = math.fabs(A)
print(math.sqrt(A))

